The present invention pertains to jack-up type marine platform structures, and more particularly to a universal footing for supporting the legs of such structures.
Marine jack-up platforms are used to form piers, causeways, and to support spanning structures which bridge between platforms. The platforms can be self-elevated to a specific height above the water surface using a jacking mechanism. In order to accommodate a wide range of seafloor types, the platforms need to be supported by footings in various seafloor soils, such as sand, silt, mud and rock.
Existing foundation systems usually rely on driven-pile foundations. In soft sediments, the total pile penetration depth can exceed 200 feet per leg. Such long pile driving and splicing operations are both time-consuming and labor-intensive. In addition, excessive shipping space is required to carry the extra piles, and shipping space is usually at a premium. In the areas of offshore drilling, exploration and production for the oil and gas industry, foundation footing types are usually pre-determined based upon site specific geotechnical data. In general, a sharp-pointed spike is used for foundations on rock or coral, while an enlarged base plate is usually selected for foundations on soft sediments.
One footing system that has been developed uses a jet eductor which generates suction-type flow for removing soil from underneath the footing through a metal strainer, so as to allow the footing to move down into the sediments. The eductor system, however, can easily be plugged up by seaweed, debris and soil containing large rocks, thereby becoming inoperative.
The instant invention, by using internal jetting to shoot water out of nozzles, avoids plugging problems, and works for clay, silt, sand, gravel, coral or rock seafloors. The jetting system of the present invention also assists in burying the footing into the seafloor, thus enhancing the overall system stability, and, in addition reduces the pullout resistance of the leg/footing upon retrieval. This invention is usefull for jetting-in various types of pilings and can be used for a variety of other marine construction.